Embedded Data Collectors

Transcription

1 Florida s Experience Presented by: Florida Department of Transportation Asst. State Geotechnical Engineer 1

2 INTRODUCTION Majority of Florida bridges are supported on deep foundations Most common deep foundation: Precast Prestressed Concrete piles Dynamic testing of all Test Piles required as per Specifications 2

3 1995 PRACTICE Pile Installation Plan (Contractor) Pre-field wave equation analysis Test Pile program Pile Driving Analyzer (PDA) CAPWAP Final wave equation Driving Criteria Install Production Piles 3

4 DRIVING CRITERIA The Driving Criteria letter as a minimum addresses the following items; Minimum number of blows per foot at various hammer stroke heights for the bearing layer Maximum allowable stroke height Minimum tip Refusal conditions Set-check requirements (when needed) 4

5 In 1996 we were asking WHAT IF? What if piles could be instrumented without climbing the leads? What if pile testing did not impact construction operations? What if all foundations could be monitored instead of issuing blow count criteria? What if all of this was affordable? 5

6 Sponsored Research Alternate dynamic testing method investigated by UF through sponsored research University of Florida s Final report issued August 2002 Proposed theory First generation hardware and software 6

7 Sponsored Research UF s Research Two levels of instruments cast into the pile, near the pile head and tip Wireless transmission to a receiver in the field 7

8 Sponsored Research UF s Research Tip/skin ratio (using top & tip instruments) 8

9 Sponsored Research UF s Research Case equation to estimate total static resistance 9

10 Sponsored Research Unloading point used to estimate static end bearing Skin Friction = Total static minus static end bearing 10

11 Sponsored Research In 2003 Smart Structures, Inc. acquired a license to the patented technology Advancements to the software, hardware and signal transmission aspects of the system 11

12 EMBEDDED DATA COLLECTOR Design Standards Index

13 EMBEDDED DATA COLLECTOR Instruments cast into solid concrete piles; Two instrumentation levels, pile head and tip 13

14 CASTING PROCESS Instrumentation Tip gages Connector cable (within the pile) Top gages and antenna 14

15 EMBEDDED DATA COLLECTOR Accelerometer Signal conditioning, temperature sensor Strain transducer 15

16 CASTING PROCESS 16

17 CASTING YARD MEASUREMENTS Install two levels of instruments prior to casting the pile Get an initial measurement to confirm signal transmission Cast the pile Subsequent measurements» Strain before and after cutting prestressing strands» Temperature readings at pile core and antenna (ambient) 17

18 Casting Yard Battery Pile Driving Battery 18

19 SOFTWARE INTERFACE Display of raw data; Strain and acceleration Qualitative assessment of data 19

20 SOFTWARE INTERFACE Display of top level instrumentation; Force-Velocity Wave up / Wave down Pile static capacity Compression and tension stresses Estimates of pile integrity (MPI) 20

21 SOFTWARE INTERFACE Tip instrumentation readings; Static force Damping & inertia (unloading point) Force-velocity at the tip of the pile Measured compressive stress near the pile tip 21

22 SOFTWARE OUTPUT 22

23 SOFTWARE OUTPUT UF and Fixed methods Minimum Tip NBR 23

24 SOFTWARE OUTPUT Top and Tip compressive stresses Max. Tension 24

25 CALCULATION METHODS Fixed Case Method Constant damping factor for the entire drive, input by operator Only top level of instruments UF Method Damping factor is calculated for every hammer blow using pile top and tip measured data 25

26 CALCULATION METHODS UF Method Continued Allows for the separation of static and dynamic resistance in real time, no signal match analysis required on an instrumented pile (top & tip) 26

27 EVALUATING RESULTS Phase I, In-House evaluation ( ) Compare EDC estimates to PDA & CAPWAP; Phase II, UF (2009 Present) Collect results and generate a database of EDC vs. static load tests to develop a system-specific resistance factor for use in LRFD design 27

28 EVALUATING RESULTS Phase 1: Compare EDC to PDA and CAPWAP Database of piles monitored simultaneously with EDC and PDA EDC data was collected and reported by different engineers than those collecting the PDA data. 28

29 EDC EVALUATION PHASE I 29

30 EDC/PDA STATIC CAPACITY Population n = 213,734 blows from 139 piles Ratio of Total Static Resistance Parameter Fixed Method/PDA UF Method/PDA Mean Median Standard Deviation Coefficient of Variation

31 EDC EVALUATION PHASE I Population n = 205,516 blows from 134 piles STRESS, ENERGY AND INTEGRITY EDC/PDA CSX CSB TSX EMX Beta Mean Median Std. Deviation Coefficient of Variation

32 EDC/CAPWAP STATIC CAPACITY Population n = 78 blows from 78 piles Ratio of Total Static Resistance Parameter Fixed Method/CAPWAP UF Method/CAPWAP Mean Median Standard Deviation Coefficient of Variation

33 EDC EVALUATION - CAPWAP 33

34 EDC EVALUATION - CAPWAP 34

35 EDC EVALUATION - CAPWAP 35

36 TIP DAMAGE INDICATOR 36

37 TIP DAMAGE INDICATOR Changes in measured strain; Observed more often near the tip of the pile Gradual loss of pre-stress as a precursor to damage Measured state of stress during driving 37

38 EVALUATING RESULTS Phase 2: Compare EDC to Static Load Tests 18 results 12 in Florida 4 in Louisiana 2 in North Carolina 38

39 EVALUATING RESULTS (2013) 39

40 EVALUATING RESULTS (2014) 40

41 IMPLEMENTATION Structures Design Guidelines

42 IMPLEMENTATION Design Bulletins issued on 2006, 2009 and 2010 addressing the use of EDC in test and production piles Collect sufficient data to evaluate the system 42

43 IMPLEMENTATION July 2011 Workbook EDC introduced as a stand-alone system (Section ) 43

44 IMPLEMENTATION 2014 Standard Specifications 44

45 IMPLEMENTATION Cost EDC instruments: $899/pile Installation: $100 (standard top/tip) Workstation lease $995/month Software lease for office use $89/month, or $961/year Pile Installation monitoring ( $500/pile, assumes two piles driven per workday) Contact Smart-Structures for details 45

46 POSSIBILITIES FOR THE FUTURE Tip + Skin = Total (no need for Case Eq. or UP) 46

47 EDC EVALUATION Summary Technology developed initially through funded research UF - Dr. Michael McVay Evaluation and stepped implementation of the system by between 2006 and

48 EDC EVALUATION Summary Top and tip gauges eliminate the need for signal matching No climbing leads Measured tip compressive stress Measured loss of pre-stress, early warning of developing pile damage 48

49 Thank you 49